Method of processing UMTS calls in a packet transmission network and node for the UMTS network and for implementing said method

ABSTRACT

In order to accept a new call for setting up in a UMTS network node, the method consists in particular in:
         calculating for the new call an equivalent passband as a function of:
           the quality of service requested for the new call; and   the quality of service attributes of the UMTS medium corresponding to the call;   
           then comparing the sum of the equivalent passband for the new call plus the equivalent passbands of all of the calls already set up in the UMTS network node with a predetermined maximum value; and   accepting the new call with guaranteed requested quality of service only if the sum is less than or equal to said predetermined maximum value.

The invention relates to a method of processing UMTS calls in a packettransmission network, and to a node for implementing the method. Theuniversal mobile telecommunications system (UMTS) is a mobile telephonesystem of the third generation. This system has a network coreconstituted by a network for transmitting data packets.

The mobile telephone system presently in use in Europe is a secondgeneration system (the GSM or “global system for mobile communications)that is essentially designed to supply telephony and data transmissionservices in circuit mode, together with a small number of remoteservices in packet mode, such as the short message service (SMS). Itcomprises a core network essentially constituted by a circuit switchednetwork. A radio subsystem serves to allocate radio traffic channels incircuit mode and to maintain the continuity of established calls formobile users by means of inter-cell transfer procedures. Quality ofservice relies mainly on the quality of the circuit switched fixednetwork.

Data services represent only a marginal fraction of the overall trafficso quality of service criteria are mainly: the probability of beingblocked during the busy hour; the call cutoff rate; and subjective voicequality. In this context, frequency planning and radio resourcedimensioning are of major importance in providing appropriate radiocoverage and traffic capacity.

Recent developments, such as adaptive multi-data rate encoding andtranscoding-free operation in the radio subsystem seek to improve thequality of service of the mobile telephone in circuit mode. With theexpansion of the Internet, general packet radio services (GPRS) havebeen introduced to provide data services that are effectively in packetmode from end to end in GSM networks. In spite of the efforts made bystandards organizations for refining the management of quality ofservice by taking account of the need to distinguish betweenapplications and subscribers, present GPRS systems are generallyconsidered as providing “best effort” service. Nevertheless, under thecontrol of the core network, it is possible to supply relative qualityof service levels.

Second generation systems were developed for conveying voice, at a timewhen 75% of the traffic carried by European operators was essentiallytelephone traffic. They were optimized to keep voice synchronization inphase and to offer telephone services by making use of a network ofintelligent architecture. The introduction of the Internet wasaccompanied by an increase in data traffic. The question now arises ofdeploying a mobile network which is adapted both to conveying Internettraffic and voice traffic.

Third generation systems will improve the situation considerably for alltypes of service (telephony, data, or multimedia services), sincequality of service management is one of the concepts underlying thespecifications drawn up in the context of the third generationpartnership project (3GPP). Third generation systems are designed to usea common transmission medium, whether radio or terrestrial, fortransporting applications in packet mode and in circuit mode.Information coming from various independent sources is multiplexed overa common transmission medium. The UMTS infrastructure should thereforecope with different kinds of traffic having bandwidth and quality ofservice requirements that are very different from one another.

The traffic generated by data transfer services and by Internet accessservices is particularly sporadic and unpredictable. Data transmissionbetween machines accommodates losses poorly but is generally notsensitive to end-to-end transmission time or jitter. In contrast,speech, and more generally all real time applications can toleratereasonable rates of loss but they require transmission times that arestrictly limited. For example, end-to-end transmission time for voicemust remain less than 400 milliseconds (ms), even when using echocancellers.

One of the main difficulties in making the UMTS infrastructure is thustransporting data for different types of application over the samemedium while complying with fixed objectives for quality of service.

In order to satisfy these requirements, the 3GPP has defined fourclasses of quality of service (Recommendation TS 23.107) respectivelyfor conversation, streaming, interactive, and background applications.The table below gives examples of applications associated with thevarious classes of quality of service, and specifies the quality ofservice attributes used for defining these classes of quality of servicein a UMTS system.

Low bit Type of Delay error Guaranteed traffic Delay variation rate bitrate Examples Conver- Strict Strict No Yes Voice over IP sational(VoIP), video traffic conferencing, audio- conferencing StreamingLimited Limited No Yes Broadcast traffic services (audio, video), news,sports Interactive Limited No Yes No Web browsing, traffic cyber chat,games, mobile trading Background No No Yes No E-mail, SMS, trafficdownloading databases, transferring measurements

It is also essential that the transmission resources of the UMTSinfrastructure should be used efficiently (radio spectrum, but alsoterrestrial transmission resources), particularly in the access portion:it must enable a transfer service to be supplied at low cost, minimizinginvestment expenditure and operating costs. It is essential to achieve astatistical multiplexing gain. In particular, it is necessary to loadthe transmission links and the radio interface to the greatest possibleextent while satisfying quality of service requirements. Consequently,the search for load optimizing is of very great importance.

One of the means for achieving such optimization is to process calls atUMTS application level. This decides whether a UMTS call can be acceptedby the UMTS call network, given the fact that it must guarantee apredetermined quality of service to an established call throughout itsduration, and that it must also maintain the quality of service forother UMTS calls that have already been established. This callprocessing is performed in all of the ports and all of the nodes of aUMTS network. Account needs to be taken of the fact that data packetsare stored temporarily in buffer memories of capacity that is limited.

The object of the invention is to propose a method of processing UMTScalls at UMTS application level which is simple, fast, efficient, androbust (i.e. which operates equally well under heavy loading as underlight loading).

The invention provides a method of processing UMTS calls in a packettransmission network, the network comprising nodes for a UMTS network,

the method being characterized in that in order to accept a new UMTScall for setting up in a UMTS network node, it consists in particularin:

-   -   calculating for the new call an equivalent passband as a        function of:        -   the quality of service requested for the new call; and        -   the quality of service attributes of the UMTS medium            corresponding to the call;    -   then comparing the sum of the equivalent passband for the new        call plus the equivalent passbands of all of the calls already        set up in the UMTS network node with a predetermined maximum        value; and    -   accepting the new call with guaranteed requested quality of        service only if the sum is less than or equal to said        predetermined maximum value.

The invention also provides a node for a packet transmission networksupporting a UMTS radio system, for implementing the method, the nodebeing characterized in that it comprises:

-   -   means for calculating for each new call an equivalent passband        as a function of:        -   the quality of service requested for the new call; and        -   the quality of service attributes of the UMTS medium            corresponding to the call;    -   means for comparing the sum of the equivalent passband for the        new call plus the equivalent passbands for all of the calls        already set up in the UMTS network node with a predetermined        maximum value; and    -   means for accepting the new call while guaranteeing the        requested quality of service only if the sum is less than or        equal to said predetermined maximum value.

The invention will be better understood and other characteristics willappear on reading the following description and the accompanyingfigures:

FIG. 1 is a block diagram of an example of a UMTS network;

FIG. 2 is a flow chart for an implementation of the method of theinvention; and

FIG. 3 shows a portion of said flow chart in greater detail.

The example UMTS network (UMTSN) shown in FIG. 1 comprises:

-   -   asynchronous transfer mode (ATM) type cross-connects, ACC1 and        ACC2;    -   a gateway GPRS support node, GGSN;    -   a serving GPRS support node, SGSN;    -   a border router BR connected to a circuit switched (CS) client        site;    -   a multimedia gateway MGW;    -   remote access nodes RNC1 and RNC2; and    -   a radio subsystem made up of base stations BTS1 and BTS2        connected respectively to the remote access nodes RNC1 and RNC2,        and connected to terminals MT by radio links.

The cross-connects ACC1 and ACC2, the gateway GPRS support node, GGSN,and the serving GPRS support nodes, SGSN are interconnected by a networkmaking use of the Internet protocol so as to constitute the core of theUMTS network.

Mechanisms for providing full support for quality of service areinstalled at all levels in the UMTS system.

At application level, call admission control is used at each node of theUMTS network. Mechanisms for managing waiting queues fairly, andmechanisms for controlling congestion, enabling the various differentqualities of service required by subscriber applications are thusperformed within:

-   -   the gateway GPRS support node, GGSN;    -   the serving GPRS support nodes, SGSN;    -   the remote access nodes RNC1 and RNC2; and    -   the multimedia gateway MGW.

In addition, a policing function is provided in the serving GPRS supportnode(s), SGSN for traffic entering the core of the network (going to thecross-connect ACC2).

At network layer level, quality of service support is performed byconventional IP differentiated services (DiffServ).

At link layer level, it is possible to use a multiprotocol labelswitching (MPLS) environment with stream labelling on interfaces knownas Gn and Gi; and it is possible to use asynchronous transfer mode (ATM)on an interface known as Iu.

Controlling call admission at application level is based on the conceptof equivalent passband. It consists in estimating the resources neededfor obtaining the requested quality of service; and in determiningwhether or not these resources are available. If they are available,then they are reserved. If they are not available, then anotherprocedure enables the requested quality of service to be reduced (ifpermitted by the application).

Call admission control is activated by the following events:

-   -   each time a UMTS or GSM call is set up in packet mode;    -   each time there is a modification to quality of service:        -   on each change of serving GPRS support node, SGSN, due to            the mobility of a subscriber.(change of quality of service            in the new node SGSN, at its initiative);        -   requested by a mobile terminal (i.e. on receiving a            change-of-context request); or        -   requested by a gateway GPRS support node, GGSN (i.e. on            receiving a request to update context);    -   on a modification in the packet stream in the radio subsystem,        at the request of said subsystem;    -   during a request for service procedure (while reestablishing a        radio access communications channel, after a service request);    -   after a procedure for updating subscription parameters leading        to a change in quality of service (on the request of the        subscriber's name register);    -   periodically, for contexts in which quality of service has been        reduced (so as to make it possible subsequently to offer a        better quality of service if new resources become available);    -   in the event of a mobile terminal being transferred between        cells (“handover”);    -   in the event of relocalization of a serving radio network        subsystem, i.e. in the event of the mobile terminal going into a        cell served by another remote access RNC node;    -   a change in the serving GPRS support node, SGSN of a mobile        terminal; or    -   a change in the gateway GPRS support node, GGSN of a mobile        terminal.

Nevertheless, in any given SGSN or GGSN node, call admission control canbe activated only by a subset of those events. Furthermore, in order toguarantee quality of service in all layers (and not only at UMTSapplication level), another call admission control takes account ofresources available in the IP transport layer. Another call admissioncontrol is also active at link layer level (ATM and/or MPLS).

At UMTS application level, certain mechanisms isolate traffic comingfrom each UMTS user equipment. By way of example, mention can be made ofmechanisms for managing queues and congestion that are implementedwithin serving GPRS support nodes, SGSN, and gateway GPRS support nodes,GGSN, or indeed the policing function and the traffic flow modelsimplemented within the GGSN node.

Ordering techniques, such as fair management of queues with waiting orcyclical ordering with waiting enable conflicts for use of a resource tobe managed. They guarantee that a certain minimum passband is allocatedto each context. They provide an implicit policing function with theadvantageous feature that this function comes into play only when thenetwork element is heavily loaded. The implicit policing is a functionthat is needed in order to be able to comply with the undertaking madewith a user concerning quality of service: if the network becomesheavily loaded, this policing function verifies that the behavior of theuser is indeed in compliance with the user's traffic contract in orderto ensure that a user whose behavior is illicit (whether deliberately orotherwise) cannot degrade the quality of service supplied to otherusers.

FIG. 2 is a flow chart of an implementation of the method of theinvention for controlling admission of a new call on entry to a UMTSnetwork node under consideration. It comprises a step of calculatingequivalent passband as a function of traffic parameters that appear inthe context of a call and that are defined by a contract with thesubscriber requesting that a call be set up. This equivalent passbandserves to represent resource requirements so as to be able to add upresource requirements and share available resources.

Step 7: A trigger event from amongst those mentioned above triggers theadmission control procedure.

Step 8: The number of activated contexts, i.e. the number of callsalready set up in the UMTS network node under consideration is comparedwith a maximum value M that is set as a function of the characteristicsof this UMTS network node; if the number of activated contexts isgreater than M:

Step 15: the request is rejected.

If the number of activated contexts is less than M:

Step 9: the requested quality of service is compared with that mentionedin the subscription contract.

If the requested quality of service level is greater than that mentionedin the subscription contract:

Step 15: the request is rejected.

If the requested quality of service is less than or equal to thatmentioned in the subscription contract:

Step 10: the equivalent passband is calculated for the new call and foreach of the calls that are already set up in the UMTS network node underconsideration, using a method described below.

Step 11: The equivalent passbands correspond to all of these calls aresummed.

Step 12: This sum is compared with the passband R that is available atthe instant under consideration in the UMTS network node underconsideration.

Step 13: If the sum is greater than R, the quality of the new call isreduced (if that is possible) or else the new call is rejected (if it isnot possible to reduce its quality).

Step 14: If the sum is less than or equal to R, the new call isaccepted, and the corresponding resources are reserved. A “CREATE PDPCONTEXT” message is sent by the serving GPRS support node, SGSN to thegateway GPRS support node, GGSN. If this node GGSN responds in thenegative because it cannot supply the requested bit rate, then theserving GPRS support node SGSN can attempt to activate the same contextin another gateway GPRS support node, GGSN. If the node GGSN reduces thequality of service, then the node SGSN modifies the data recordedconcerning the resources that have been reserved.

When a context is deactivated (end of a call or movement of a user), itsequivalent passband is no longer taken into account in step 11 ofsumming passbands.

FIG. 3 shows, in greater detail, the operation 10 of calculating theequivalent passband corresponding to a call. This particular procedureis given by way of example. The method of the invention can beimplemented with other procedures for calculating equivalent passband.

Step 20: Starting the procedure for calculating equivalent passband onthe basis of the context of a call.

Step 21: Testing the class of traffic contained in the context:

If the traffic is conversational:

-   -   Step 22: Calculating the equivalent passband using the formula:        EB=Min[MBR, GBR+alpha(MBR−GBR)], where MBR is the maximum bit        rate, and GBR is the guaranteed bit rate, which are quality of        service attributes, and which form part of the context of the        new call, and where alpha is a constant;    -   Step 23: end of procedure.

If the traffic is not conversational: Step 24: test the class of trafficcontained in the context.

If the traffic is streaming:

-   -   Step 25: calculate the equivalent passband using the formula:        EB=Min[MBR, GBR+beta(MBR−GBR)], where beta is a constant;    -   Step 23: end of the procedure.

If the traffic is not streaming: Step 26: test the class of trafficcontained in the context.

If the traffic is interactive:

-   -   Step 27: calculate the equivalent passband using the formula:        EB=MRB·b where b is a constant which is a function of the        processing priority level of the traffic (a value which is fixed        by default or fixed by a network manager);    -   Step 23: end of the procedure.

If the traffic is not interactive:

-   -   Step 28: calculating the equivalent passband using the formula:        EB=Min(C0, MBR) where C0 is a constant of small value, e.g. 10        bits per second;    -   Step 23: end of the procedure.

The constants alpha, beta, b, and C0 are selected by the operator of thenetwork as a function of network management policy. The values of theparameters MBR, GBR, and the other quality of service attributes formpart of the context of each call and they are compared with contractualvalues for the same parameters stored in the name location register thatmanages the subscriber requesting that a call be set up. For variousUMTS media services, quality of service attributes are given in thetable below for each class of traffic.

Traffic class Conversational Streaming Interactive Background Attributestraffic traffic traffic traffic Maximum bit X X X X rate MBR Delivery inX X X X the right order Maximum size X X X X of a service data unit(SDU) SDU format X X information SDU error X X X X rate Residual bit X XX X error rate Return of X X X X erroneous SDUs Transfer X X delayGuaranteed X X bit rate GBR Traffic X processing priority Allocation/ XX X X retention priority

The function of controlling call admission can be used within an SGSN ora GGSN node to verify that the resources needed for setting up a callare available in the node. However they could also be used from outsidea node in order to verify that the interfaces Gn, Iu, and Gi of the nodehave the necessary resources. Consequently, the equivalent passband Ractually available in a node can be equal:

-   -   either to the equivalent passband of the processor of the node,        SGSN or GGSN;    -   or to the equivalent passband of an ATM virtual circuit on an        interface Iu, Gn, Gi;    -   or the physical passband of a link or of a router;    -   or the passband of an MPLS tunnel on a Gn or Gi interface;    -   or the passband of a DiffServ class (EF or Afx or BE) or of a        group of classes.

Firstly, the quality of service allocated to a call may be reduced toits contractual value in autocratic manner, if the requesting terminalhas requested a quality of service greater than the contractual value.During the call, the actual quality of service may be increased ordecreased, but it is always less than or equal to that initiallyrequested when setting up the call in question.

A procedure for reducing quality of service is called when the requestedequivalent passband is not available. For conversational traffic and forstreaming traffic, the procedure for reducing quality of service can bebased only on reducing the guaranteed bit rate. The requestingapplication may refuse such a reduction, or it may accept it and thenselect another encoding algorithm or another coder in order to becapable of operating with a passband that is smaller than thatrequested. The decision is taken by the final user, not by the network.

For traffic that is interactive or streaming, the procedure for reducingquality of service is based on the processing priority that has beenrequested for the traffic. If the requested equivalent passband is notavailable, then the quality of service is reduced to correspond to thenearest level below the processing priority of the traffic. If therequested equivalent passband is still not available when the quality ofservice is reduced in this way, then background traffic class may beproposed to the user.

Quality of service is never increased above the contractual value. Calladmission control can be called when changing the serving GPRS supportnode, SGSN due to the subscriber moving. Quality of service might thenbe increased as a function of the quality of service initiallyallocated, or the quality of service negotiated by an earlier SGSN node.Similarly, but only for calls which have had their quality of servicereduced, quality of service may be increased by periodically calling thecall admission control function in order to be able to offer a betterquality of service if resources become available.

Call admission control may also be a function of a parameter referred toas allocation/retention priority, which is defined in the subscriptioncontract. It enables certain subscribers to be given priority whensetting up calls, e.g. VIPs, fire brigades, police services, etc. If therequested passband is not available, call admission control can decide:

-   -   to reduce quality of service (while retaining the same class of        service), in the event of the allocation/retention priority        parameter not being used by the network operator;    -   to attempt to supply the requested passband by making use of the        allocation/retention priority parameter to select amongst calls        that have already been set up, a call that is to be interrupted;        or    -   to use the allocation/retention priority parameter during a        procedure between serving GPRS support nodes SGSN: if the        parameter is equal to a medium value, and only for a call that        has already been set up, the new node may attempt to conserve        the quality of service negotiated by the preceding SGSN node. To        do this, it may interrupt certain calls having the lowest        allocation/retention priority.

1. A method of processing UMTS calls in a packet transmission network,the network comprising UMTS network nodes; the method beingcharacterized in that in order to accept a new UMTS call for setting upin a UMTS network node, it consists in particular in: calculating forthe new call an equivalent passband as a function of: the quality ofservice requested for the new call; and the quality of serviceattributes of the UMTS medium corresponding to the call; then comparingthe sum of the equivalent passband for the new call plus the equivalentpassbands of all of the calls already set up in the UMTS network nodewith a predetermined maximum value; and accepting the new call withguaranteed requested quality of service only if the sum is less than orequal to said predetermined maximum value.
 2. A method according toclaim 1, characterized in that implementation is triggered in particularby one of the following events; a request to set up a call in UMTS orGSM packet mode; a change of quality of service, initiated by a mobileterminal or by the network; a change of radio subsystem (BTS, RNC)serving a mobile terminal; a change in the gateway GPRS support node(GGSN) of a mobile terminal; or a change in the serving GPRS supportnode (SGSN) of a mobile terminal.
 3. A method according to claim 1,characterized in that it further consists in reducing quality of servicewhen the requested equivalent passband is not available; in that forconversational and streaming traffic, a reduction in quality of serviceis based on reducing guaranteed bit rate; and in that for interactive orstreaming traffic, the procedure for reducing quality of service isbased on the processing priority that has been requested for thetraffic; and in that if the requested equivalent passband is still notavailable when the quality of service is reduced, then background classtraffic is proposed to the user.
 4. A method according to claim 1,characterized in that if the quality of service guaranteed to a call isless than that requested, it consists in periodically repeating theoperations specified in claim 1 to offer a better quality of service ifresources have become available.
 5. A node for a UMTS network, for apacket transmission network supporting a UMTS radio telephone system,the UMTS network node being characterized in that it comprises: meansfor calculating for each new call an equivalent passband as a functionof: the quality of service requested for the new call; and the qualityof service attributes of the UMTS medium corresponding to the call;means for comparing the sum of the equivalent passband for the new callplus the equivalent passbands for all of the calls already set up in theUMTS network node with a predetermined maximum value; and means foraccepting the new call while guaranteeing the requested quality ofservice only if the sum is less than or equal to said predeterminedmaximum value.
 6. A UMTS network node according to claim 5,characterized in that the means for calculating equivalent passband foreach new call are triggered by: a request to set up a call in UMTS orGSM packet mode; a change of quality of service, initiated by a mobileterminal or by the network; a change of radio subsystem (BTS, RNC)serving a mobile terminal; a change in the gateway GPRS support node(GGSN) of a mobile terminal; or a change in the serving GPRS supportnode (SGSN) of a mobile terminal.
 7. A UMTS network node according toclaim 5, characterized in that it further comprises means for reducingquality of service when the requested equivalent passband is notavailable; in that for conversational and streaming traffic, a reductionin quality of service is based on reducing guaranteed bit rate; and inthat for interactive or streaming traffic, the procedure for reducingquality of service is based on the processing priority that has beenrequested for the traffic; and in that if the requested equivalentpassband is still not available when the quality of service is reduced,then said means for reducing quality of service propose a backgroundclass of traffic to the user.
 8. A UMTS network node according to claim5, characterized in that it further comprises means for use, if thequality of service of a call is less than that requested, to compareperiodically the sum of the equivalent passband requested for the newcall and the equivalent passband for all of the calls already set up inthe UMTS network node with a predetermined maximum value, and to offer abetter quality of service if resources have become available.